Optical network failure recovery method

Abstract

An optical network failure recovery method for a passive optical network is provided. The method includes steps of: obtaining at least one round-trip delay value according to an equalization delay value of at least one optical network unit with respect to an operating optical line terminal; sorting the round-trip delay values in an increasing order and obtaining a minimum round-trip delay value; obtaining at least one difference between the minimum round-trip delay value and the round-trip delay value of each of the optical network units; and adjusting a start time and a stop time in a bandwidth map for a ranging response message replied by each of the optical network units according to the at least one difference.

What is claimed is: 
     
       1. An optical network failure recovery method for a passive optical network, comprising:
 obtaining at least one round-trip delay (RTD) value according to an equalization delay (EqD) value of an optical network unit (ONU) with respect to an operating optical line terminal (OLT); 
 sorting the RTD value in a predetermined order, and obtaining a minimum RTD value; 
 obtaining at least one difference between the minimum RTD value and the RTD value of each ONU; and 
 adjusting a start time and a stop time in a bandwidth map for a ranging response message replied by each ONU according to the difference; 
 wherein, when a failure of the optical network occurs, the start time and the stop time are utilized in a ranging step for each ONU. 
 
     
     
       2. The optical network failure recovery method according to  claim 1 , wherein the difference represents a time difference between the ranging response message replied by each ONU to the operating OLT and the ranging response message replied by the ONU located at a minimum distance from the operating OLT to the operating OLT. 
     
     
       3. The optical network failure recovery method according to  claim 1 , wherein the passive optical network is an ITU Telecommunication Standardization Sector (ITU-T) type B architecture. 
     
     
       4. The optical network failure recovery method according to  claim 3 , wherein a failure recovery period of the type B architecture less than 50 ms. 
     
     
       5. The optical network failure recovery method according to  claim 1 , wherein the EqD value is measured by ranging each ONU with respect to the OLT, and the measuring step comprises:
 the OLT transmitting a ranging request message to each ONU; 
 the ONU replying the ranging request message to the OLT; and 
 the OLT calculating the at least one EqD value. 
 
     
     
       6. The optical network failure recovery method according to  claim 1 , wherein the RTD value is a difference between a zero-distance equalization value and the EqD value. 
     
     
       7. The optical network failure recovery method according to  claim 1 , wherein the start time is added with a predetermined period or a system parameter to prevent overlapping or a collision caused by a range response. 
     
     
       8. The optical network failure recovery method according to  claim 7 , wherein the system parameter comprises 13 bytes needed by the ranging response, a guard band needed by the OLT, and an error when measuring the RTD value. 
     
     
       9. The optical network failure recovery method according to  claim 1 , wherein the start time and the stop time are predetermined before the failure of the optical network occurs.